In the fields of measurement and data acquisition, problems exist when the measurement data is to be obtained from rotary members of operating machinery such as, for example, a turbine rotor. Slip rings have commonly provided the only effective means of acquiring large quantities of data from strain gages, thermocouples, and other transducers which may be mounted on the rotating part. Increasingly, however, computer-based data reduction techniques are being applied and the attendant demand for higher quality signals has manifested problems inherent in the use of slip rings. The most severe problem results from variability in contact resistance between slip ring and contact brush. This imposes distortion and noise on signals as they pass between ring and brush so that costly processing is then required to extract the measurement information.
There are other problems known to be involved in the use of slip rings and brushes. For example, brushes have a short, unpredictable operating life span, and often, the number of rings and brushes which can be physically accommodated severely limits the channel capacity of a data acquisition system. While radio telemetry has been a useful alternative to slip rings where only a limited number of measurements are to be made, it is costly, complex, and not the optimum solution for multichannel, large data handling requirements.
Another problem in acquiring measurement data from rotating machinery arises from the frequent need to make measurements under widely different operating conditions. For example, it may be desired to measure strain under normal operating conditions and, at some other time, repeat the measurement under high stress, abnormal conditions. It is important therefore that the measuring instrument be adaptable to those changing conditions without requiring the operating machine to be shut down to effect the adaptation.
Accordingly, it is an object of the present invention to provide an improved, multichannel data acquisition system for rotating machinery that avoids both slip rings and radio telemetry as the means for data transfer.
It is another object of the invention to provide a multi-channel data acquisition system in which circuitry, rotatable with a machine member upon which measurements are to be made, is powered by an induced high-frequency power signal.
A further object of the invention is to provide a contactless multichannel data acquisition system for rotating machinery in which the measurement sensitivity range can be selected during machinery operation.